The present invention relates generally to a process for reacting high molecular weight polyols with alkenyl halides to produce alkenyl ethers according to the Williamson synthesis. More particularly the present invention relates to a method for forming allyl ethers from high molecular weight polyols reacted with allyl chloride to produce allyl ethers in the presence of flaked sodium hydroxide and entraining solvent such as toluene to produce high yields of the allyl ether. Reaction conditions include: generally atmospheric pressure, a liquid system utilizing a concentrated alkali metal hydroxide, a water immiscible hydrocarbon solvent such as toluene and a high molecular weight polyol in which the hydroxyl groups are the sole functional groups and the alcohol is free from aliphatic unsaturation. Product recovery involves a two phase liquid system for washing the product and later a stripping of the water immiscible solvent since the product is not readily distillable from the reaction solution. Such a method permits the production of allyl ethers without the use of costly components such as dimethylsulfoxide and high pressures associated with processes of past practice.
The Williamson synthesis reaction discovered in 1850 is still the best general method for the preparation of unsymmetrical ethers or for that matter symmetrical ones. The production of an alkenyl ether by this process involves the reaction of a sodium alkoxide with an alkenyl halide such as allyl chloride which evidentally involves an attack of the alkoxide ion upon the polarized carbon-halogen bond in the alkenyl halide by a nucleophic substitution mechanism of the second order. Many of the more complex alkenyl ethers can be prepared in this fashion from polyols with alkenyl halides but the substantial commercial exploration of such a method has been militated against by the cost of some of the materials and ultimately the resultant product. Another problem has been that the reaction conditions have been rather extreme in some cases such as: requiring high pressures, the fact that many of the higher molecular weight materials and the ethers thereby produced are not readily distillable from the reaction mixture. This second problem makes the recovery of a pure product difficult.
Some lower molecular weight materials have been produced from polyols by using an allyl bromide in an excess of 50 percent aqueous sodium hydroxide solution at elevated temperatures. These ethers result when polyols containing free hydroxyl groups are reacted with a hydrocarbon halide, with a halogen preferably bound directly to an aliphatic carbon atom, in the presence of an amount of alkali metal hydroxide at least equivalent to the amount of hydrocarbon halide used. Dimethylsulfoxide is used as a solvent at a temperature up to the boiling point of the dimethylsulfoxide.
The use of allyl chloride has been proposed for substitution in such reactions to yield allyl ethers, but the problem here is that the pressures used in this type of reaction are rather substantial in addition to achieving a rather low yield of product. Furthermore, large excesses of material are used to achieve even moderate yields. Allyl chloride would be preferable to the bromides because of costs.
Thus, it would be extremely advantageous to be able to produce higher molecular weight alkenyl ethers utilizing alkenyl chlorides as a reactant to accomplish good yields under such reaction conditions as to make the process a commercially viable production reaction. Furthermore, it would be advantageous to be able to recover alkenyl ethers which are not readily distillable from the reaction mixture.